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Desiccant Quantity Calculator

Work out desiccant quantity instantly with clear inputs, formula shown and shareable results.

About Desiccant Quantity Calculator

Desiccant must absorb both the moisture sealed inside with the air and the moisture permeating through the pack over the protection period. Silica gel adsorbs roughly 20% of its own weight at moderate humidity, so the mass required is total water divided by that capacity.

Formulas

Moisture load

Ingress = WVTR x pack area x days; enclosed air moisture = volume (L) x 0.0173 g/L at 23 C, 60% RH

Desiccant mass

Desiccant = total water / adsorption capacity (0.2 for silica gel)

Worked example

With the default values below, Desiccant Quantity Calculator returns Desiccant Required of 14.773. Change any input above and every figure here is recalculated in your browser.

Inputs used

Pack Internal Volumeminimum 0 L
2 L
Package WVTRminimum 0 g/m2/day
0.05 g/m2/day
Pack Surface Areaminimum 0 m2
0.08 m2
Protection Periodminimum 0.01 days
730 days

Results

Desiccant Required
14.773
Moisture Ingress Over Period
2.9200
Moisture In Enclosed Air
0.0346
10 g Sachets Required
2

Step by step

  1. 1Values used
  2. 2Moisture load
  3. 3Desiccant mass
  4. 4Desiccant Required= 14.773
  5. 5Moisture Ingress Over Period= 2.9200
  6. 6Moisture In Enclosed Air= 0.0346
  7. 710 g Sachets Required= 2

Assumptions and limits

  • The result is derived only from the 4 inputs listed above. Anything not among them is not part of the calculation.
  • In particular, this calculator does not take inflation, tax or fees or charges into account.
  • Figures are rounded for display to 4 decimal places, so totals built from several rounded parts can differ slightly from the unrounded arithmetic.

How these calculators are built and tested is described on the Methodology page. If a figure looks wrong, please report it.

Frequently Asked Questions

Is silica gel always the right desiccant?

Molecular sieve holds more at low humidity and is better for very dry requirements; clay is cheaper for less demanding uses; calcium oxide is used for very long-term protection. Match the isotherm to the target humidity.

Why include the sealed-in air?

For a small pack it can dominate. One litre of air at 23 C and 60% RH carries about 12 mg of water, which is significant when the total budget is a few hundred milligrams.

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